McConnell’s nod on Tuesday came hours after House Speaker John A. Boehner of Ohio stepped off the sidelines to endorse Romney after months of avoiding the topic.

“We’re all behind him,” McConnell said. “He’s going to be the nominee. As you have noticed, the party is in the process of unifying behind him.”

Boehner in particular had avoided the almost weekly questions on the issue in part because he had worked in the House and had differences with then-Speaker Newt Gingrich, who remains in the race. Boehner also sought neutral ground because of his role as convention chairman. But on Tuesday the speaker joined the party establishment in coalescing around its expected top choice.

“It's clear now Mitt Romney is going to be our nominee,” Boehner said. “I think Mitt Romney has a set of economic policies that can put Americans back to work, and frankly, contrast sharply with the failed economic policies of President Obama. And I will be proud to support Mitt Romney and do everything I can to help him win."